A portable electronic device, such as a conventional notebook computer, is approximately the size of a standard sheet of paper, (21.6 cm by 27.9 cm; or in English units, 8.5 inches by 11.0 inches). The thickness of such a notebook computer typically ranges from 1.9 cm to 6.0 cm or more. In efforts to increase transportability and usability, the evolution has been toward smaller, lighter portable computers. The typical notebook computer includes a display screen housing hinged to a keyboard housing. The display screen housing folds down against the keyboard where the two housings latch together. A processor board, keyboard and disk drive often are mounted within the keyboard housing. Additional features include input/output ports and one or more compartments for receiving PC cards, (i.e., peripheral devices conforming to the personal computer memory card international association (PCMCIA) standards for personal computer-based peripherals). In an effort to bring multimedia applications to the notebook computer, loudspeakers and sound cards also may be included.
The shortcoming of loudspeakers used within notebook computers or other portable electronic devices is the generally inferior sound quality achieved relative to conventional stereophonic shelf-top speakers, or even, internal or external speakers used with desktop computers. One reason for the poorer sound quality is the relatively smaller speaker sizes. The smaller speaker size makes it difficult to produce quality sound over a wide frequency range, and particularly at lower frequencies. Coupled with the restricted speaker-box volume in which the loudspeaker is housed, quality sound at lower frequencies is difficult to achieve. Larger speaker-boxes provide space for accommodating given wavelengths of sound waves. Increasing the size of a notebook computer to accommodate significant speaker-box sizes is undesirable, however. Such inclusion would be a trade-off on the transportability of the computer. Accordingly, there is a need for a speaker configuration in a portable electronic device such as a notebook computer which improves sound quality without increasing the size requirements of the computer housing.
One attempt to solve this problem is disclosed in commonly assigned U.S. Pat. No. 5,668,882 to Hickman et al. This patent discloses the use of a lower frequency speaker mounted within the keyboard housing, in addition to two higher frequency speakers mounted in the display housing. While effective at solving this problem mentioned above, the additional cost associated with the lower frequency speaker may not be desirable in all circumstances.